Squared end section for air supported structure

ABSTRACT

The air inflated envelope of a square end section of an air supported structure is reinforced by a cabling system providing for relatively uniform distribution of longitudinal stress to the envelope of the central section of the structure. The cabling system may be employed to reduce the longitudinal stress loading to a value less than pr.2.

United States Patent [191 Bird [ SQUARED END SECTION FOR AIR SUPPORTED STRUCTURE [75] Inventor: Walter W. Bird, Williamsville, N.Y.

[73] Assignee: Birdair Structures, Inc., Buffalo,

[22] Filed: Aug. 27, 1973 [21] Appl. No.: 392,093

[52] US. Cl. .t 52/2 [51] Int. Cl E04b 1/345 [58] Field of Search 52/2, 80

[56] References Cited UNITED STATES PATENTS 3,416,762 12/1968 Headrick 52/2 3,651,609 3/1972 Bird 52/2 3,661,693 5/1972 Pierson r 52/2 3,728,831 4/1973 Bird i 52/2 3,772,836 11/1973 Geiger 52/80 July 8, 1975 FOREIGN PATENTS OR APPLICATIONS l,l83,483 3/1970 United Kingdom 52/2 1,235,093 3/1960 France 52/2 OTHER PUBLICATIONS Popular Science pages 73-75, August, 1971.

Primary Examiner-Ernest R. Purser Assistant Examiner-Henry Raduazo Attorney, Agent, or Firm-Bean & Bean 5 7 1 ABSTRACT The air inflated envelope of a square end section of an air supported structure is reinforced by a cabling system providing for relatively uniform distribution of longitudinal stress to the envelope of the central section of the structure. The cabling system may be employed to reduce the longitudinal stress loading to a value less than pr.2.

14 Claims, l2 Drawing Figures PATENTED JUL 8 ms SHEET ma u PATENTEQJUL v 8 I975 SHEET 1 SQUARED END SECTION FOR AIR SUPPORTED STRUCTURE BACKGROUND OF THE INVENTION Air inflated structures having end sections of spherical surface or circular plan form base line configuration, which are attached to the ends of a partial generally cylindrically shaped central section are well known in the art. A decided drawback of these structures is that they cannot be tailored for use in covering a rectangular area, without there being either an excess of unnecessary floor space and/or useless floor space adjacent the base line of the ends of the structures.

The drawback of this type of air inflated structure led to my development of air inflated structures having squared ends, that is, end sections having essentially squared corners, whereby to provide a structure having an essentially rectangular plan view configuration. In one form of this development, which is disclosed in my US. Pat. No. 3,728,831, each of the end sections is formed with a generally cylindrical end portion bounded by small, generally spherical corner portions in order to maximize head room usable space for a given covered area. By proper patterning of the end section envelope portion and by the utilization of a cabling system including tension transmitting cables disposed to extend lengthwise of the central section, it is possible to construct a squared end structure with almost any proportions, while keeping longitudinal stress values applied to the central section envelope portion relatively low and somewhat uniformly distributed hoopwise thereof.

However, it has been found that for certain installations, such as large tennis enclosures requiring seasonal erection and handling, a simplified cabling arrangement, as well as more head room or vertical clearance adjacent the base line of the end section was needed.

SUMMARY OF THE INVENTION The present invention is directed towards an improved squared end section for use with an air inflated structure. More specifically, the present invention is directed towards the utilization of a simplified cabling system for use in providing relatively uniform distribution of longitudinal stress from the envelope portion of a squared end section to the envelope portion of a central section at points spaced hoopwise of the latter and for providing for reduction of longitudinal stress values to less than pr/2.

In accordance with the present invention, flexible tension devices, such as cables, are fixed to the end section envelope portion to extend transversely of the structure and have their opposite ends fixed to the ground anchorage. Elements of the end section envelope between cables are patterned so as to transfer es sentially all hoopwise directed envelope loadings transversely into the cables, i.e., longitudinally of the structure, for subsequent transfer by the cables to the ground anchorage. The cables, although placed under tension upon inflation of the end section envelope, are constrained thereby to assume a double curvature configuration when viewed in the plane of the envelope. By this arrangement, the cables additionally serve to pick up end or lengthwise directed loadings from the relatively highly stressed top or central portion of the envelope and redistribute such loadings to the lower side portions of the envelope. As a result, there is achieved a longitudinal stress distribution at points hoopwise of the central section, which approximates the uniform distribution of longitudinal stress obtained for a noncable reinforced spherically shaped end section.

The value of longitudinal stress applied to the central section may be reduced below a value of pr/Z by arranging the opposite ends of the end section cables to lie within planes intersecting the plane of the ground anchorage at values of less than 90.

DRAWINGS The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein:

FIG. 1 is a side view of an air inflated structure incorporating squared end sections of the present invention;

FIG. 2 is an end view thereof;

FIG. 3 is a partial plan view thereof;

FIG. 4 is an enlarged view of the area designated generally as FIG. 4 in FIG. 1;

FIG. 5 is a sectional view taken generally along line 5-5 in FIG. 2;

FIGS. 6A and 6B are diagrammatic views illustrating the distribution of longitudinal stress for a non-cabled rounded end section and a non-cabled squared end section, respectively;

FIGS. 6C and 6D are diagrammatic views illustrating the distribution of longitudinal stress for alternative forms of the improved cabled, squared end section of the present invention;

FIG. 7A is a diagrammatic view illustrating the stress distribution in an envelope attached to bowed cable;

FIG. 7B is a diagrammatic view illustrating the stress distribution in an envelope attached to a cable having a double curvature;

FIG. 7C is a diagrammatic view illustrating the stress distribution in an envelope attached to a cable having a double curvature, but differing end conditions.

DETAILED DESCRIPTION Reference is now made to FIGS. 1 through 3 wherein an air inflated structure is generally designated as 10 and shown as including a partial generally cylindrically shaped central section 12 and a pair of essentially squared corner end sections 14, which are formed in accordance with the present invention. Erection and disassembly of the structure may be facilitated by removably joining the end sections to the central section in areas, designated as 16, by any suitable means, such as joiner devices of the type disclosed in prior US. Pat. Nos. 3,116,746 and 3,103,050. In a like manner, the central section may be formed from a plurality of individual sections in order to permit the central section to be selectively constructed in multiples of some given, easily handled length. The placement of the joiner devices is a mere matter of choice and design convenience.

It will be understood that one of the end sections may be dispensed with in a situation where for instance the central section is to be employed as an extension of a rigid building structure. Also, the central section may be dispensed with and only one end section employed as a rigid building extension. In either of these cases, it would of course be necessary to seal the remaining air inflated portion of the structure to the building as well as to the ground anchorage.

Preferably, the central section is formed in the manner disclosed in my prior US. Pat. No. 3,651,609. More specifically, the central section would be defined by an air inflatable envelope portion 18 formed by a plurality of relatively narrow, horizontally elongated panels 20, which have their adjacent marginal edge portions arranged in an overlapping. attached relationship with vertically adjacent panels; and a cable system having a plurality of parallel, relatively widely spaced, flexible tension devices, such as cables 22, which extend transversely of the structure and have their opposite ends suitably connected or anchored to a ground anchorage. While the present structure is normally installed to extend or arch upwardly from adjacent ground level, as indicated in FIGS. 1, 2 and 4, it will be understood that the term "ground anchorage" as used herein is meant to also include walls to which the ends of the cables could be attached and about which the lower edges of the structure are suitably air sealed. The structure is particularly adapted to cover large areas; the central section being for instance 120 feet in width and of any desired length.

As in my prior U.S. Pat. No. 3,651,609, envelope panels are preferably fabricated from conventional low cost envelope forming fabric, which is characterized as being elastic or extensible substantially only in its fill or transverse direction. For purposes of reference, it will be understood that this type of fabric is relatively narrow when compared to the spacing between adjacent cables 22, e.g. 4 feet wide as compared to spacings of normally between about 12 to 20 feet. When employing envelope panels of this type, a circular element 180 of central section envelope portion 18, i.e. a hoop-wise extending segment of the envelope between any pair of adjacent cables, is free to stretch vertically or hoopwise into a toroidally shaped configuration under normal inflation pressure. In that the envelope material is designed and/or the envelope patterning developed to provide for stretch or extensibility in the vertical or hoopwise direction and to resist stretch in the horizontal or longitudinal direction, substantially all of the panel loads will be transferred equally to adjacent cables, which in turn directly transfer such loads to the ground anchorage. In addition to loads due to inflation pressure, panel loads would include aerody namic and snow loads.

As the central section would be designed such that primary loading in the vertical or hoopwise direction is carried almost entirely by the cables, the maximum vertical load in the circular elements 180 is very small and there is no need to employ a conventional catenary system to attach the envelope to the ground anchorage. However, in order to keep the envelope material smooth and wrinkle free, to carry localized aerodynamic loadings which may develop, and to uniformly position the lower edges of the envelope adjacent the ground anchorage, it is preferable to thread a suitable cable, not shown, through a sleeve, also not shown, formed in the lowermost panels and suitably affix such cable to the ground anchorage.

Again referring to FIGS. 1-3, it will be understood that each of squared end sections 14 generally includes an air inflatable envelope portion 24; and a cable system having a plurality of flexible tension devices, such as cables 26. In order to permit proper inflation of envelope portion 24, its opposite side and outermost marginal edges of envelope portion 24 are suitably air sealed relative to the ground anchorage, whereas an innermost marginal edge of envelope portion 24, which arches upwardly over the ground anchorage is suitably air sealed relative to a hoopwise extending end edge of central section envelope portion 18. Also, it will be understood that cables 26 extend transversely of their associated end section and have their opposite ends suitably connected or anchored to the ground anchorage adjacent their associated end section envelope side marginal edges.

In a preferred construction, envelope portion 24 includes inner, one or more intermediate and outer envelope elements 24a, 24b and 24c, respectively. which are arranged to extend transversely of the structure in a marginally edge joined relationship, and a pair of partial generally spherically shaped corner elements 24d. which are joined to opposite ends of outer element 24(- and a relatively outer transversely extending marginal edge of an immediately adjacent intermediate element 24b. Intermediate elements 24b arch upwardly over the ground anchorage and have surfaces, which approximate serpentine portions of the surface of a generally toroidal shape, which in turn would appear to approximate a torus. Relatively innermost and outermost envelope elements 240 and 240, respectively have surface configurations somewhat similar to that of elements 24b, except that their relatively inner and outer transversely extending marginal edges are essentially "straight" when viewed in plan in that they are attached to the central section in area 16 (or in effect to the endmost of the central section cables 22) and to the ground anchorage, respectively. Cables 26 are connected to the end section envelope to lie one along each of the adjacent transversely extending marginal edges of elements 24a, 24b and 240, and thus such cables arch upwardly over the ground anchorage between their opposite ends, which are fixed to the ground anchorage adjacent opposite side marginal edges of the end section envelope, as shown in FIGS. 1-3.

Envelope elements 24a, 24b and 24c are preferably formed by a plurality of relatively narrow, elongated, marginally edge joined panel 28, which extend transversely of cables 26. Panels 28 may be arranged in end alignment with central section panels 20 much in the same manner as that proposed for use in connection with the end sections of the structure disclosed in above mentioned U.S. Pat. No. 3,651,609. In practice, it is convenient to form panels 28 from short panel lengths, which are end joined in an overlapping relationship, as by heat or adhesive bonding in the manner indicated in FIG. 5. Also, the edges of the panel lengths may be tapered or patterned as required to develop the desired toroidal shape of the envelope elements.

As in the case of the central section, the end section envelope panels are preferably formed from a conventional fabric or material capable of being extensible in its fill or transverse direction to provide for stretch in a direction transversely of the structure. Thus, substantially all hoopwise or transversely directed end section envelope loads resulting from inflation pressure, as well as aerodynamic and snow loadings, are carried transversely of the toroidally shaped envelope elements (lengthwise of the structure) into their bounding cables and the ground anchorage in the case of element 24c and then by such cables transversely of the structure into the ground anchorage. Alternatively, the material forming the envelope elements may be relatively inextensible, but patterned to permit the elements to assume a generally toroidal shape wherein the material is tensioned sufficiently to carry inflation loadings substantially only in a transversely direction into the bounding cables. Since in either case substantially all of the hoopwise direction loads on the envelope elements 240 and 24b are transferred into their bounding cables, their opposite ends as in the case of central section envelope elements 180, need not be ground anchored by a conventional catenery system. However, a catenery system or clamping device must be employed to attach the lower or relatively outer transversely extending marginal edge of outer element 246 to the ground anchorage.

Corner elements 24a, which are inheritently stable, due to their essentially spherically shaped surface configuration, are formed with relatively small radii of curvature roughly approximating the radii of curvature of the toroids or tori from which envelope elements 24a, 24b and 240 are developed. In actual practice, corner elements 24d do not define true spherical surfaces in that they are intentionally patterned to optimize transfer of local loads to the adjacent cable, to maximize usable head room adjacent the corners of the base line and to smoothly blend with the end surfaces of outer envelope element 240. As a result, elements 24d may bulge or balloon outwardly so as to partially mask opposite ends of an adjacent intermediate element, as illustrated in FIG. 2. Corner elements 24d, which may be formed from several panels 29 in the manner disclosed in U.S. Pat. No. 3,728,831 are attached to the ground by a conventional catenery system. As a practical design matter, since the nature of the corner elements dictates that they carry loads in two directions, slight loading may be imparted to opposite ends of envelope element 24c with the result that it tends to flatten out or become somewhat cylindrical particularly at its midpoint and thus its surface departs from that of a true tomid.

Cables 26, which are best shown in FIG. 3, as having a double (or reverse) curvature, may be characterized as being of serpentine or sinusoidal configuration when viewed in the plane of the envelope. The cables may be individually attached to the end section envelope in any suitable manner, but for purposes of illustration are shown in FIG. 5 as being frictionally retained within a sleeve device 30, which is in turn suitably affixed to the outer surface of the envelope, as by adhesive bonding. The sleeve device may, if desired, be of the type disclosed in U.S. Pat. No. 3,728,831.

To permit a more complete understanding of the present invention and the benefits derived therefrom, reference is now made generally to FIGS. 6a through 70. Specifically, reference is first made to FIG. 6a, which illustrates the manner in which end section produced longitudinal stress is distributed hoopwise of the end of the envelope of the central section of an air inflated structure in the case where the end section of the structure is non-cabled and of partial, generally spherically shaped configuration. This longitudinal stress, which results from inflation pressure acting against the envelope of the end section in a direction lengthwise or longitudinally of the air inflated structure, is represented by the expression pr/2, where p is the inflation pressure and r is the radius of curvature of the central section. It will be noted that for this type of end section, which may be characterized as having a circular plan view configuration or a semi-circular base line, the longitudinal stress transferred across the innermost marginal edge of its envelope to the end or hoopwise extending marginal edge of the central section envelope is distributed in a substantially uniform manner.

FIG. 6b illustrates the longitudinal stress distribution, which would characterize a non-cabled end section of essentially squared corner plan view configuration. As will be apparent, longitudinal stress applied to the envelope of a central section, due to pressure acting against the envelope of a squared end section, is not uniformly distributed as in the case of a circular plan view end section, but varies from a value approximating zero adjacent the side base lines or ground anchor age to a value which may approach pr along the top (or center line or mid-portion) of the envelope for the case where the corners of the base line are essentially square. it will be understood that the areas bounded by the longitudinal stress curve in FIGS. 60 and 6b are essentially equal for a given inflation pressure and radius; and that the shape of the longitudinal stress curve of FIG. 6b may be varied by progressively increasing the radius of curvature of the corners in order to progressively increase the longitudinal stress developed on the lower sides of the envelope adjacent the base line and achieve a corresponding reduction in the value of longitudinal stress developed at the central portion of the envelope, as the plan form of the end section approaches the circular plan form of FIG. 60. With a noncabled, squared end section, it would not be possible to develop in the envelope elements of a cabled central section a uniform curvature between their bounding cables (in order to provide for uniform and controlled envelope stresses), since the curvature off the elements of the central section will at any point hoopwise thereof be directly proporportional to the value of the longitudinal stress developed in the end section at such hoopwise point.

The very high longitudinal stress developed at the central portion of the envelope in the case of squared end sections is undesirable in that it results in a lower factor of safety and greater vulnerability to damage when compared to a like sized spherical end section, and thus for a given envelope material places a distinct limitation on the size of the structure with which a noncabled, squared end section may be employed. For a given envelope material, the permissible size of a squared end section may be increased by employing a cable reinforcing system of the type disclosed in U.S. Pat. No. 3,728,831. A drawback, however, is the need for employing tension transmitting cables extending lengthwise of the central section to carry a part of the end section loading, which would otherwise be transmitted in the form of longitudinal stress to the envelope of the central section.

FIG. 60 illustrates the relatively uniform stress distribution, which may be achieved with the cabled, squared end section of the present invention without the necessity of employing the more complex cabling system required in U.S. Pat. No. 3,728,831.

FlG. 6d is similar to FIG. 6c, except that it illustrates that the cable system of the present invention may be patterned to reduce the longitudinal stress applied to the envelope of the central section to a maximum value less than pr/Z.

The manner in which the novelly designed cable sys tem of the present invention is employed to effect a relatively uniform distribution of longitudinal stress and, if required, the reduction thereof will now be more fully described with reference to FIGS. 7a-7c. Before specifically referring to FIGS. 7a-7c, it should be noted that these Figures are merely diagrammatic views showing ideal" envelope stress distributions obtainable when cables of different configurations are attached to an envelope surface. While the ideal stress distributions shown by these views will be influenced to some degree by the interaction of all forces, due to inflation pressures acting on an actual envelope of curved surface configuration, they are, however, believed helpful in understanding the overall effect of the sev' eral forms of the cabling system of the present invention on longitudinal stress developed in a squared end section. The actual stress distribution present in any given end section envelope configuration can be empirically determined.

Now, with particular reference to FIG. 70, it will be understood that if an end anchored flexible cable is attached to an unstressed envelope, such that the cable is bowed or assumes an arcuate configuration, subsequently applied cable loads, which are induced in an actual envelope installation by inflation pressures will serve to tension the cable such that the latter will tend to straighten out. The tendency of the cable to straighten out will be resisted by loads developed in the envelope in reverse proportion to the curvature of the cable. If the ends of the deflected cable intersect their end or ground anchorage at an angle less than 90, the loading of the cable will be transferred to the ground anchorage as an end loading L,, which may be divided into components L and L The above principal applies in a case wherein for instance a cable is attached to the surface of a spherically or cylindrically shaped envelope to lie within a plane other than a plane of a great circle. Thus, in the design of air inflated structures every attempt is normally made to place reinforcing cables such that they lie within great circle planes when the envelope is inflated in order to avoid unduly stressing the envelope and realizing surface deformation thereof (reference the cable arrangement employed in above mentioned US. Pat. No. 3,651,609). A notable exception to those is where cables are used to reinforce around openings, such as doors, where the cable is attached to the envelope and is shaped so as to pick up the loads in the envelope and transfer them around the opening with a minimum of distortion in the envelope and resultant concentration of stress.

Reference is now made particularly to FIG. 7b, which shows an end anchored cable having a double (or reverse) curvature, that is, a serpentine or sinusoidal shaped configuration, attached to an envelope; the ends of the cable being arranged to intersect the end or ground anchorage at an angle of 90. When the cable is loaded in the manner described above in connection with FIG. 7a, the tendency for the cable to straighten out will again be resisted by loads developed in the envelope, but this time there will be a redistribution of envelope loads, due to the reverse curvature of the cable. In the uniform double curvature arrangement illustrated in FIG. 7b, the cable picks up loads adjacent its central portion (adjacent opposite sides of the line designated CL) and redistributes or applies such loads equally to opposite side portions of the envelope, such that the area within the load curve above the central portion of the cable is equal to the sum of the areas within the load curves below the end portions of the cable. Further, it will be noted that with the arrangement illustrated in FIG. 7b, the cable loadings are carried straight into the ground, as by aligned end loadings I...

The arrangement illustrated in FIG. 7b is uniquely applied in accordance with the present invention by employing reversely curved cables to pick up loads from the more highly stressed central portion of the envelope of the square end section and redistribute such loads to the opposite or lower side portions thereof adjacent the base line. in order to achieve an essentially uniform longitudinal stress distribution curve illustrated in FIG. 6c, wherein the maximum longitudinal stress approximates a value of pr/2. It will be understood that the specific shape of each of cables 26 may be determined and thus the distribution of load may be effectively controlled once the proper shape of the envelope has been analytically or experimentally determined; consideration being given to head room requirements, acceptable fabric stresses, aesthetic appearance etc. Also, it will be understood that in this form of the present invention, the ends of cables 26 would be arranged within a plane, which extends transversely of the structure and intersects the plane of the ground anchorage at an angle of such that end loadings L are transferred into the ground without there being developed any horizontal component of force in a direction lengthwise of the structure. Thus, while this form of the present cabling system is effective in redistributing the longitudinal stress, as generally indicated in FIG. 6c, it has no effect on the total longitudinally directed load applied to the central section envelope and accordingly, the areas under the stress curves shown in FIGS. 6b and 6c are essentially equal.

The above described cable configuration is referred to as being of double curvature" or reverse curvature when viewed in the plane of the envelope, but in fact the cable is also curved in a direction transversely of the structure.

Reference is now made to FIG. 70, which illustrates a cable arrangement similar to that of FIG. 7b, except that the degree of curvature of each of the cable end portions is less than that of the central or mid-portion of the cable and the ends of the cable intersect the end or ground anchorage an an angle other than 90; such that cable end loading L. is divided into load components L and L In this arrangement, the sum of the areas of the curves beneath the end portions of the cable is less than the area of the stress curve over the midportion of the cable by an amount corresponding to the value of load L transmitted to the ground anchorage. Thus, loading of the envelope is both redistributed and reduced by the fact that a portion of the cable loading is transferred into the ground anchorage in a direction aligned with the direction of loading of the envelope. The theory discussed in connection with FIG. 70, is put to use in accordance with the preferred form of the present invention by arranging the ends of at least certain and preferably all of cables 26 lie within transverse planes disposed to incline upwardly towards the outer end of the end section, such that they intersect a plane defined by the ground anchorage at angles less than 90 and horizontal components of load L are developed in a direction lengthwise of the structure, as

indicated in FIG. 4. Accordingly. it will be understood that cables 26 may be shaped to achieve a redistribution of longitudinal stress in order to provide for essentially uniform distribution thereof, as well as to effect a reduction in overall end loading, as will be apparent from viewing FIG. 6d. This arrangement permits relatively inexpensive lower strength fabric to be safely used in forming relatively large square ended sections.

By again referring to FIG. 7c, it will be understood that, as the curvature of the end portions of the cable is reduced, such that the end portions assume essentially straight line configurations between the curved mid portion of the cable and the ground anchorage, the area of the stress curves under the end portions of the cable will be progressively reduced to zero; there being a corresponding increase in the value of load coomponents L While a squared end section reinforced by a cable having a curved mid portion and straight end portions will not serve to increase envelope loadings adjacent the opposite sides of the end section, it will serve to render the distribution of longitudinal stress more uniform and effect a reduction in total end loading, due to the fact that loads are removed from the highly stressed central portion of the end section envelope and transferred into the ground anchorage as load components L This type of cable configuration can be considered as being of single curvature" when viewed in the plane of the envelope, but in fact the cable also curves in a direction transversely of the structure.

At present, it is envisioned that this latter or single curvature type of cable configuration would normally be employed only in situations where envelope loadings or longitudinal stress adjacent opposite sides of the end section envelope are already relatively large on account of forming corner elements 24d with a relatively large radius of curvature. In this connection, it will be remembered that it is desirable to maintain the hoopwise distribution of longitudinal stress as uniform as possible in order to permit relatively uniform curvature of the envelope elements of a cabled central section with which the square end section is associated. Thus, a squared end section reinforced with straight ended cables may posses somewhat less utility in that for most anticipated installations it is desirable to maintain the corner elements at the smallest radius consistent with head room requirements and aesthetic appearance of the structure.

From the foregoing description, it will be understood that the terms squared end section or square ended section merely refer to end sections having a generally rectangular plan form configuration, wherein opposite sides and the outermost base lines or marginal edges of the envelope are essentially straight. Further, it will be understood that the term square or squared" corner is meant to include arrangements wherein the outermost base line is joined to the opposite side base lines by rounded" corner base lines, as well as where the outermost base line actually intersects the opposite side base lines at an angle of essentially 90.

While the illustrated end section construction, which employs four envelope elements and three cables, has been found in practice to provide a structurally practical and aesthetically pleasing configuration for squared end sections having base line or footprint dimensions on the order of about 53 X 120 feet, it will be understood that the present invention is not limited thereto.

In this respect, it is specifically contemplated that an end section having only inner, outer and corner envelope elements and a single cable may be advantageously employed.

Also, while the illustrated squared end section construction features a horizontally patterned envelope, it will be understood that the present invention is not limited thereto. In this respect, it will be appreciated that the disclosed cabling arrangement may be employed to achieve longitudinal stress redistribution and/or reduction at least to some degree even for a conventional vertically or hoopwise patterned envelope, so long as such envelope serves to maintain the cables in a tensioned condition and to constrain same in their disclosed curved configuration.

I claim:

I. An air inflated structure adapted to overlie a ground anchorage, which comprises in combination:

a central section having an air inflatable envelope portion of partial, generally cylindrically shaped surface configuration, said central section envelope portion arching upwardly over said ground anchorage and having lengthwise extending lower edges fixed in an air sealed relationship relative to said ground anchorage and hoopwise extending end edges; and

a pair of end means joined to said hoopwise extending end edges of said central section envelope portion for closing opposite ends of said central section at least one of said end means being an air inflated end section including an air inflated envelope portion of essentially square corner plan view configuration air sealed relative to said central section envelope portion and at least one flexible tension device, said end section envelope portion having an innermost, opposite side and outermost marginal edges, said innermost marginal edge arching upwardly over said ground anchorage and being fixed in an air sealed relationship to one of said end edges of said central section envelope portion, said opposite side and outermost marginal edges being fixed in an air sealed relationship relative to said ground anchorage, said tension device having opposite ends thereof fixed to said ground anchorage adjacent said opposite side marginal edges, said tension device extending transversely of said end section envelope portion and arching upwardly over said ground anchorage between said opposite ends thereof, said tension device being fixed to said end section envelope portion, said end section envelope portion maintaining said tension device in a tensioned condition and constraining same in a reverse curved configuration relative to the surface thereof for causing said tension device to pick up inflation pressure induced end section envelope portion loadings directed lengthwise of said structure from relatively high stress central portions of said end section envelope portion disposed intermediate said opposite side marginal edges and to redistribute at least a portion of such loadings to relative low stress opposite side portions thereof.

2. A structure in accordance with claim 1, wherein said tension device has said opposite ends thereof arranged to lie within a plane extending transversely of said structure and intersecting a plane defined by said ground anchorage at an angle less than for developing a horizontal component of load in a direction lengthwise of said structure for diminishing inflation pressure induced end section loadings applied to said central section envelope portion.

3. A structure in accordance with claim 1, wherein said central section additionally includes at least one tension means fixed to said envelope portion thereof adjacent said end section to extend transversely of said structure with opposite ends of said one tension means connected to said ground anchorage. said end section envelope portion includes a plurality of transversely extending envelope elements having partial generally toroidally shaped surface configurations and a pair of corner elements having partial generally spherically shaped surface configurations, a relatively innermost of said envelope elements defining said innermost marginal edge of said end section envelope portion and being connected therealong to said tension means, a relatively outermost of said envelope elements defining said outermost marginal edge of said end section envelopeportion, relatively outer and inner transversely extending marginal edges of adjacently disposed envelope elements being joined together, one said tension device being fixed to said end section envelope portion to lie along each of said joined marginal edges, said envelope elements other than said outermost envelope element arching upwardly over said ground anchorage and having opposite ends thereof air sealed relative thereto, and each of said corner elements having marginal portions thereof joined to an end of said outermost envelope and joined to a relatively outer transversely extending marginal edge of an envelope element to which a relatively inner transversely extending marginal edge of said outermost element is joined outwardly of said end thereof and fixed to said ground anchorage.

4. An air inflated structure adapted to overlie a ground anchorage which comprises in combination:

a central section having an air inflated envelope portion of partial generally cylindrically shaped surface configuration, said central section envelope portion arching upwardly over said ground anchorage and having lengthwise extending lower edges fixed in an air sealed relationship relative to said ground anchorage and hoopwise extending end edges; and

a pair of end means joined to said hoopwise extending end edges of said central section envelope portion for closing opposite ends of said central section, at least one of said end means being an air inflated end section, said end section including an air inflated envelope portion marginally fixed in an air sealed relationship to one of said end edges of said central section envelope portion along an innermost marginal edge thereof and said ground anchorage along opposite side and outermost marginal edges thereof to assume a squared corner plan view configuration and at least one flexible tension device extending transversely of said structure and having opposite ends fixed to said ground anchorage adjacent said opposite side marginal edges, said tension device arching upwardly over said ground anchorage between said opposite ends, said tension device being fixed to said end section envelope portion for tensioning said tension device and for effecting a relatively uniform distribution of inflation pressure induced end section envelope portion loading applied to said central section envelope portion across said one of said end edges to which said end section envelope portion is fixed.

5. An air inflated structure according to claim 4, wherein said one tension device is of reverse curved configuration and has said opposite ends disposed within a vertical plane extending transversely of said structure and intersecting a plane defined by said ground anchorage at an angle of substantially 6. An air inflated structure according to claim 4, wherein said one tension device has said opposite ends disposed within a plane extending transversely of said structure and being vertically inclined to extend upwardly in a direction outwardly toward said outermost marginal edge whereby to intersect a plane defined by said ground anchorage at an angle of less than 90 for developing a horizontal component of load in a direction lengthwise of said structure for diminishing said inflation pressure induced end section envelope portion loading.

7. An air inflated structure according to claim 6, wherein said tension device is a cable having a reverse curved configuration relative to the surface of said end section envelope portion.

8. In a structure including an air inflated section joined to an other part of said structure, said section having an air inflated envelope of essentially squared corner plan view configuration fixed in an air sea ed relationship relative to a ground anchorage along, opposite side and outermost marginal edges thereof and relative to said other part along an innermost marginal edge of said envelope arching upwardly over said ground anchorage characterized in that inflation induced loadings in said envelope are transferred across said innermost marginal edge into said other part, the improvement comprising:

at least one flexible tension device fixed to said envelope and arranged to extend transversely of said section, said tension device having opposite ends fixed to said ground anchorage adjacent said opposite side marginal edges of said envelope and arching upwardly over said ground anchorage between said opposite ends, said tension device being tensioned and constrained by said envelope to have a reverse curved configuration relative to the surface of said envelope for redistributing said loadings to reduce and increase values of said loadings transferred across said inner marginal edge adjacent mid and opposite side portions thereof, respectively.

9. The improvement in accordance with claim 8, wherein said opposite ends of said tension device are arranged to lie within a plane, said plane extending transversely of said section and being vertically inclined to extend upwardly in a direction towards said outermost marginal edge of said envelope, whereby to intersect a plane defined by said ground anchorage at an angle less than 90 10; In a structure including an air inflated section joined to an other part of said structure, said section having an air inflated envelope of essentially squared corner plan view configuration fixed in an air sealed relationship to a ground anchorage and said other part, the improvement comprising:

said envelope being characterized as including inner,

at least one intermediate and outer envelope elements extending transversely of said structure and a pair of corner elements of partial generally spherically shaped surface configuration, said inner and intermediate and outer envelope elements having adjacently disposed transversely extending relatively inner and outer marginal edges joined together, said inner envelope element and said intermediate envelope element arching upwardly over said ground anchorage and having opposite ends thereof air sealed relative thereto, said intermediate envelope element having a surface approximating a serpentine portion of the surface of a toroid wherein said relatively inner and outer marginal edges thereof have a curved configuration relative to the surface of said envelope, said inner envelope element having a surface approximating a portion of the surface of a toroid and having said relatively outer marginal edge thereof joined to said relatively inner marginal edge of an adjacent intermediate envelope element and having said relatively inner marginal edge thereof joined to said other part, said outer element having a surface approximating a portion of the surface of a toroid and having said relatively inner marginal edge thereof joined to said relatively outer marginal edge of an adjacent intermediate envelope element and having said relatively outer marginal edge thereof fixed in an air sealed relationship relative to said ground anchorage, and said corner elements being marginally joined one to each end of said outer envelope element and to said relatively outer marginal edge of said intermediate envelope element arranged adjacent to said outer envelope element transversely outwardly of said ends of said outer envelope element and being fixed in an air sealed relationship relative to said ground anchorage; and

a plurality of flexible tension devices extending transversely of said structure with opposite ends thereof fixed to said ground anchorage, and said tension devices being fixed to said envelope one along each of said adjacently disposed marginal edges of said envelope elements and maintained in a tension condition by inflation pressure acting on said envelope for effecting a relatively uniform distribution of inflation pressure induced envelope loading applied to said other part across said relatively inner marginal edge of inner envelope element.

11. The improvement according to claim 10, wherein said opposite ends of said tension devices lie within planes extending transversely of said structure, at least certain of said planes being vertically inclined to extend upwardly and in a direction toward said outer envelope element, whereby to intersect a plane defined by said ground anchorage at an angle less than 90.

12. In a structure including an air inflated squared corner section joined to an other part of said structure, said section including an air inflated envelope having essentially straight opposite side and outermost marginal edges joined by rounded corner marginal edges defined by partial generally spherically shaped corner portions of said envelope, said opposite side, outermost and rounded corner marginal edges being fixed in an air sealed relationship relative to a ground anchorage,

said envelope being air sealed relative to said other part along an innermost marginal edge thereof joiningg said opposite side marginal edges and arching upwardly over said ground anchorage characterized in that inflation induced end loadings on said envelope are transferred across said innermost marginal edge into said other part, the improvement comprising:

at least one flexible tension device fixed to said envelope and arranged to extend transversely of said section, said tension device having opposite ends fixed to said ground anchorage adjacent said oppo site side marginal edges and arching upwardly over said ground anchorage between said opposite ends. said opposite ends being arranged to lie within a plane extending transversely of said section, said plane being vertically inclined to extend upwardly in a direction towards said outermost marginal edge whereby to intersect a plane defined by said ground anchorage at an angle less than and said tension device being tensioned and constrained by said envelope to have a curved configuration relative to at least a central portion of the surface of said envelope disposed intermediate said opposite side marginal edges for reducing the value of said loadings in said central portion of said envelope tranferred across said innermost marginal edge into said other part.

13. The improvement according to claim 12, wherein said tension device is constrained by said envelope to have a configuration wherein curvature of said tension device relative to opposite side portions of said envelope is the reverse of curvature thereof relative to said central portion.

14. A method of employing a flexible tension device for redistributing stress between areas of an air inflated envelope of curved surface configuration otherwise characterized as having when inflated a relatively high stress area bounded on opposite sides thereof by relatively low stress areas, said stress being directed essentially normal to a plane passing in sequence through one of said low stress areas, said high stress area and the other of said low stress areas, which comprises:

attaching said tension device to said envelope to extend transversely in succession through one of said low stress areas, said high stress area and the other of said low stress areas and to constrain said tension device from movement when said envelope is inflated from a configuration wherein curvature of said tension device in said high stress area is the reverse of curvature of said tension device in said low stress areas when viewed in the plane of said envelope;

fixing opposite ends of said tension device against movement; and

inflating said envelope to place said tension device in a tension condition, the tendency of said tension device when tensioned to become straightened serving to redistribute stress from said high stress area to said low stress areas.

* IF l 

1. An air inflated structure adapted to overlie a ground anchorage, which comprises in combination: a central section having an air inflatable envelope portion of partial, generally cylindrically shaped surface configuration, said central section envelope portion arching upwardly over said ground anchorage and having lengthwise extending lower edges fixed in an air sealed relationship relative to said ground anchorage and hoopwise extending end edges; and a pair of end means joined to said hoopwise extending end edges of said central section envelope portion for closing opposite ends of said central section at least one of said end means being an air inflated end section including an air inflated envelope portion of essentially square corner plan view configuration air sealed relative to said central section envelope portion and at least one flexible tension device, said end section envelope portion having an innermost, opposite side and outermost marginal edges, said innermost marginal edge arching upwardly over said ground anchorage and being fixed in an air sealed relationship to one of said end edges of said central section envelope portion, said opposite side and outermost marginal edges being fixed in an air sealed relationship relative to said ground anchorage, said tension device having opposite ends thereof fixed to said ground anchorage adjacent said opposite side marginal edges, said tension device extending transversely of said end section envelope portion and arching upwardly over said ground anchorage between said opposite ends thereof, said tension device being fixed to said end section envelope portion, said end section envelope portion maintaining said tension device in a tensioned condition and constraining same in a reverse curved configuration relative to the surface thereof for causing said tension device to pick up inflation pressure induced end section envelope portion loadings directed lengthwise of said structure from relatively high stress central portions of said end section envelope portion disposed intermediate said opposite side marginal edges and to redistribute at least a portion of such loadings to relative low stress opposite side portions thereoF.
 2. A structure in accordance with claim 1, wherein said tension device has said opposite ends thereof arranged to lie within a plane extending transversely of said structure and intersecting a plane defined by said ground anchorage at an angle less than 90* for developing a horizontal component of load in a direction lengthwise of said structure for diminishing inflation pressure induced end section loadings applied to said central section envelope portion.
 3. A structure in accordance with claim 1, wherein said central section additionally includes at least one tension means fixed to said envelope portion thereof adjacent said end section to extend transversely of said structure with opposite ends of said one tension means connected to said ground anchorage, said end section envelope portion includes a plurality of transversely extending envelope elements having partial generally toroidally shaped surface configurations and a pair of corner elements having partial generally spherically shaped surface configurations, a relatively innermost of said envelope elements defining said innermost marginal edge of said end section envelope portion and being connected therealong to said tension means, a relatively outermost of said envelope elements defining said outermost marginal edge of said end section envelope portion, relatively outer and inner transversely extending marginal edges of adjacently disposed envelope elements being joined together, one said tension device being fixed to said end section envelope portion to lie along each of said joined marginal edges, said envelope elements other than said outermost envelope element arching upwardly over said ground anchorage and having opposite ends thereof air sealed relative thereto, and each of said corner elements having marginal portions thereof joined to an end of said outermost envelope and joined to a relatively outer transversely extending marginal edge of an envelope element to which a relatively inner transversely extending marginal edge of said outermost element is joined outwardly of said end thereof and fixed to said ground anchorage.
 4. An air inflated structure adapted to overlie a ground anchorage which comprises in combination: a central section having an air inflated envelope portion of partial generally cylindrically shaped surface configuration, said central section envelope portion arching upwardly over said ground anchorage and having lengthwise extending lower edges fixed in an air sealed relationship relative to said ground anchorage and hoopwise extending end edges; and a pair of end means joined to said hoopwise extending end edges of said central section envelope portion for closing opposite ends of said central section, at least one of said end means being an air inflated end section, said end section including an air inflated envelope portion marginally fixed in an air sealed relationship to one of said end edges of said central section envelope portion along an innermost marginal edge thereof and said ground anchorage along opposite side and outermost marginal edges thereof to assume a squared corner plan view configuration and at least one flexible tension device extending transversely of said structure and having opposite ends fixed to said ground anchorage adjacent said opposite side marginal edges, said tension device arching upwardly over said ground anchorage between said opposite ends, said tension device being fixed to said end section envelope portion for tensioning said tension device and for effecting a relatively uniform distribution of inflation pressure induced end section envelope portion loading applied to said central section envelope portion across said one of said end edges to which said end section envelope portion is fixed.
 5. An air inflated structure according to claim 4, wherein said one tension device is of reverse curved configuration and has said opposite ends disposed within a vertical plane extending transversely of said structure and intersecting a plane defined by said ground anchorage at an angle of substantially 90 *.
 6. An air inflated structure according to claim 4, wherein said one tension device has said opposite ends disposed within a plane extending transversely of said structure and being vertically inclined to extend upwardly in a direction outwardly toward said outermost marginal edge whereby to intersect a plane defined by said ground anchorage at an angle of less than 90* for developing a horizontal component of load in a direction lengthwise of said structure for diminishing said inflation pressure induced end section envelope portion loading.
 7. An air inflated structure according to claim 6, wherein said tension device is a cable having a reverse curved configuration relative to the surface of said end section envelope portion.
 8. In a structure including an air inflated section joined to an other part of said structure, said section having an air inflated envelope of essentially squared corner plan view configuration fixed in an air sealed relationship relative to a ground anchorage along opposite side and outermost marginal edges thereof and relative to said other part along an innermost marginal edge of said envelope arching upwardly over said ground anchorage characterized in that inflation induced loadings in said envelope are transferred across said innermost marginal edge into said other part, the improvement comprising: at least one flexible tension device fixed to said envelope and arranged to extend transversely of said section, said tension device having opposite ends fixed to said ground anchorage adjacent said opposite side marginal edges of said envelope and arching upwardly over said ground anchorage between said opposite ends, said tension device being tensioned and constrained by said envelope to have a reverse curved configuration relative to the surface of said envelope for redistributing said loadings to reduce and increase values of said loadings transferred across said inner marginal edge adjacent mid and opposite side portions thereof, respectively.
 9. The improvement in accordance with claim 8, wherein said opposite ends of said tension device are arranged to lie within a plane, said plane extending transversely of said section and being vertically inclined to extend upwardly in a direction towards said outermost marginal edge of said envelope, whereby to intersect a plane defined by said ground anchorage at an angle less than 90 *.
 10. In a structure including an air inflated section joined to an other part of said structure, said section having an air inflated envelope of essentially squared corner plan view configuration fixed in an air sealed relationship to a ground anchorage and said other part, the improvement comprising: said envelope being characterized as including inner, at least one intermediate and outer envelope elements extending transversely of said structure and a pair of corner elements of partial generally spherically shaped surface configuration, said inner and intermediate and outer envelope elements having adjacently disposed transversely extending relatively inner and outer marginal edges joined together, said inner envelope element and said intermediate envelope element arching upwardly over said ground anchorage and having opposite ends thereof air sealed relative thereto, said intermediate envelope element having a surface approximating a serpentine portion of the surface of a toroid wherein said relatively inner and outer marginal edges thereof have a curved configuration relative to the surface of said envelope, said inner envelope element having a surface approximating a portion of the surface of a toroid and having said relatively outer marginal edge thereof joined to said relatively inner marginal edge of an adjacent intermediate envelope element and having said relatively inner marginal edge thereof joined to said other part, said outer element having a surface approXimating a portion of the surface of a toroid and having said relatively inner marginal edge thereof joined to said relatively outer marginal edge of an adjacent intermediate envelope element and having said relatively outer marginal edge thereof fixed in an air sealed relationship relative to said ground anchorage, and said corner elements being marginally joined one to each end of said outer envelope element and to said relatively outer marginal edge of said intermediate envelope element arranged adjacent to said outer envelope element transversely outwardly of said ends of said outer envelope element and being fixed in an air sealed relationship relative to said ground anchorage; and a plurality of flexible tension devices extending transversely of said structure with opposite ends thereof fixed to said ground anchorage, and said tension devices being fixed to said envelope one along each of said adjacently disposed marginal edges of said envelope elements and maintained in a tension condition by inflation pressure acting on said envelope for effecting a relatively uniform distribution of inflation pressure induced envelope loading applied to said other part across said relatively inner marginal edge of inner envelope element.
 11. The improvement according to claim 10, wherein said opposite ends of said tension devices lie within planes extending transversely of said structure, at least certain of said planes being vertically inclined to extend upwardly and in a direction toward said outer envelope element, whereby to intersect a plane defined by said ground anchorage at an angle less than 90*.
 12. In a structure including an air inflated squared corner section joined to an other part of said structure, said section including an air inflated envelope having essentially straight opposite side and outermost marginal edges joined by rounded corner marginal edges defined by partial generally spherically shaped corner portions of said envelope, said opposite side, outermost and rounded corner marginal edges being fixed in an air sealed relationship relative to a ground anchorage, said envelope being air sealed relative to said other part along an innermost marginal edge thereof joiningg said opposite side marginal edges and arching upwardly over said ground anchorage characterized in that inflation induced end loadings on said envelope are transferred across said innermost marginal edge into said other part, the improvement comprising: at least one flexible tension device fixed to said envelope and arranged to extend transversely of said section, said tension device having opposite ends fixed to said ground anchorage adjacent said opposite side marginal edges and arching upwardly over said ground anchorage between said opposite ends, said opposite ends being arranged to lie within a plane extending transversely of said section, said plane being vertically inclined to extend upwardly in a direction towards said outermost marginal edge whereby to intersect a plane defined by said ground anchorage at an angle less than 90*, and said tension device being tensioned and constrained by said envelope to have a curved configuration relative to at least a central portion of the surface of said envelope disposed intermediate said opposite side marginal edges for reducing the value of said loadings in said central portion of said envelope tranferred across said innermost marginal edge into said other part.
 13. The improvement according to claim 12, wherein said tension device is constrained by said envelope to have a configuration wherein curvature of said tension device relative to opposite side portions of said envelope is the reverse of curvature thereof relative to said central portion.
 14. A method of employing a flexible tension device for redistributing stress between areas of an air inflated envelope of curved surface configuration otherwise characterized as having when inflated a relatively high stress area bounded on opposite sides theReof by relatively low stress areas, said stress being directed essentially normal to a plane passing in sequence through one of said low stress areas, said high stress area and the other of said low stress areas, which comprises: attaching said tension device to said envelope to extend transversely in succession through one of said low stress areas, said high stress area and the other of said low stress areas and to constrain said tension device from movement when said envelope is inflated from a configuration wherein curvature of said tension device in said high stress area is the reverse of curvature of said tension device in said low stress areas when viewed in the plane of said envelope; fixing opposite ends of said tension device against movement; and inflating said envelope to place said tension device in a tension condition, the tendency of said tension device when tensioned to become straightened serving to redistribute stress from said high stress area to said low stress areas. 